How Abundant Is Iron in the Core of the Perseus Cluster?

Abstract

The analysis of Perseus data collected with the Medium-Energy Concentrator Spectrometer (MECS) on board BeppoSAX shows that the ratio of the flux of the 8 keV line complex (dominated by Fe Kβ emission) to the 6.8 keV line complex (dominated by Fe Kα emission) is significantly larger than predicted by standard thermal emission codes. Moreover, the analysis of spatially resolved spectra shows that the above ratio decreases with increasing cluster radius. We find that, among the various explanations that we consider, the most likely requires the plasma to be optically thick for resonant scattering at the energy of the Fe Kα line. We argue that if this is the case, then measures of the iron abundance made using standard thermal emission codes that assume optically thin emission may significantly underestimate the true iron abundance. In the case of the core of Perseus, we estimate the true abundance to be ~0.9 solar in a circular region with a radius of ~60 kpc and centered on NGC 1275. Finally, we speculate that similar results may hold for the core of other rich clusters.